The invention relates to a gripper rapier provision for weaving machines which work according to the principle of split rapiers.
With such weaving machines, the so-called rapier weaving machines, rapier rods are disposed on either side of the weaving machine in order to insert the weft threads. The total insertion cycle is divided into three phases: the presenting phase, the insertion phase and the pulling-through phase. During the insertion phase the rapiers move together on the forward path out of a starting position to the middle of the fabric and on the return path from the middle to the starting position. In the starting position the weft thread is presented to a donor rapier. In the middle of the fabric, the weft thread is taken over by a gripper rapier and with the return movement the weft thread is pulled through from the middle of the fabric up to the fell of the fabric.
The gripper rapier can for example consist of a fixed gripper rapier body provided with a hook with a gripping face on the inside of the hook, and of a hinged clip suspended from that fixed gripper rapier body, which with a gripping face thereon works together with the gripping face of the hook in order to grip a weft thread taken by the gripper rapier.
The Belgian patent publication no. 844 865 describes such a gripper rapier which is used for the weft insertion. That gripper rapier consists of a hook for pulling the weft thread out of the donor rapier, and in that hook a hinged clip is mounted in order to keep the weft thread gripped during the pulling-through phase.
In practice it appears that gripper rapiers known from the state-of-the-art can cause problems.
Thus during the insertion phase the weft thread is initially accelerated from standstill from the starting position up to a high speed; because of this a tensile force develops in the weft thread as a result of the mass inertia of the yarn. When reaching a high insertion speed a resistance providing force develops in the weft thread as a result of the friction arising in the guiding eyes. The clamping in the gripper rapier must be capable of overcoming these tensile forces with sufficient safety.
The Belgian patent publication no. 844 865 describes a few measures for this purpose: an opening is provided on the hinged clip and a projecting rib is provided on the wedge surface of the hook in order to clamp the weft thread onto ribbed surfaces. When the tensile force in the weft thread becomes great the clamped weft thread slides further under the clip and is in this manner pulled out of the clip. This causes a weft insertion fault and this is detected by the weft check device of the weaving machine which generates a stop signal. The efficiency of the weaving machine will therefore decrease.
With the increasing weaving machine speeds and especially when weaving heavy jute threads in yarn number range from 210 tex to 2.times.840 tex, this problem becomes rather acute. As a measure the clamping pressure can be increased by incorporating a stronger spring with higher spring pretension. The thread clip however has to be pressed open at the end of the pulling-through phase and for this a greater pressure force is then required in order to release the weft thread. This causes wear and tear on the operating surfaces. When the clamping pressure is made too high a thick weft thread is difficult to pull into the clamping wedge during the middle takeover. Furthermore the gripper hook can fail under the too great a clamping pressure, through which the hook top breaks off. It is very important to keep the mass of the gripper rapier as low as possible, to lessen the mass effect of the rapier rods, a strengthening of the gripper hook is therefore not an adequate solution.
A further problem can arise at the end of the pulling-through phase, when the gripper clip is pressed open in order to release the inserted weft thread. During the last number of cm movement of the gripper rapier the released weft thread is pulled out of the gripper hook, whereby the weft end is guided in a loop between the open clip and the gripper hook. When a bulge or a knot is present in the weft yarn end that has to be pulled out, the weft yarn remains sticking in the open gap between clip and gripper rapier hook. With the next stop movement of the weaving reed the piece of weft thread is pulled and the broken-off yarn end remains sticking in the rapier hook. With the next takeover of a new weft thread to be inserted the weft thread is no longer clamped and this is the cause of a standstill of the weaving machine for weft thread breakage. Because of this the efficiency of the weaving machine decreases. This phenomenon frequently occurs when weaving carpets where the use of thick jute yarns is common. In a bobbin of jute yarns there are many knots and also bulges. This gives rise to frequent stoppages of the weaving machine for weft thread breakage.
The moment at which the moving rapier releases the weft thread with the gripper rapiers according to the state-of-the-art also appears not always to be the correct one, and the rapier clip is not always sufficiently open, and it also does not remain sufficiently uniformly open during a part of the path of the still moving rapier. In fact the weft thread should be able to be released with a still moving rapier, so that the weft yarn can already be pulled out of the clip out of a still moving rapier.
The gripper rapier heads according to the state-of-the-art therefore also have the following two deficiencies:
the release gap is too narrow to allow bulges or knots through; PA1 the opening of the clip does not remain constant during the movement of the rapier. PA1 a fixed gripper rapier body provided with a hook and a gripping face on the inside of the hook, and PA1 a hinged clip suspended from the fixed gripper rapier body, which with a gripping face thereon, works together with the gripping face of the hook in order to grip a weft thread taken by the gripper rapier provision, PA1 whereby in front of the extremity of the gap formed by the gripping face of the hinged clip and the gripping face of the hook a mechanism is provided which prevents the weft thread from sliding to the extremity of the gap.